In many applications where the detection of light signals, particularly coherent light signals or laser signals, is desirable, it is also important to be able to detect such signals arriving at the detector from all directions. Since sensors inherently have limited fields of view, sensor heads are employed which may focus signals originating outside a sensor's nominal field of view onto the sensor for detection.
The use of an optical sensor head to focus peripheral signals onto the sensor has several advantages over other choices such as increasing the number of sensors. First, a properly designed sensor head will likely be much less expensive than the cost of adding sensors and the associated electronics. Second, in applications where the electronic complexity of additional sensors is undesirable, fewer sensors with larger fields of view offer a favorable design option.
Although the choice of increasing the sensor's field of view offers economic and practical advantages over the choice of increasing the number of sensors, designing the proper sensor head is not without difficulties, particularly where the detection of coherent signals is concerned. Optical sensor head designs which employ a multiplicity of individual sensor heads cause their own problems, particularly where the sensor must detect laser signals.
Among the problems associated with a multiple head design are the complicated optics required to keep internal scattering at a minimum and still provide a large field of view for the detector. If the sensor is to detect laser signals internal reflections may result in a loss of coherence of the incident signal. Further, as a result of the complicated optics, losses of signal strength may be unacceptably high. Finally, even with a multiple-head design the field of view may be inadequate for a particular application.
What is need, then, is a design for the optical sensor head which optimizes the field of view without suffering from the above-mentioned defects. Such a solution must offer a favorable economic trade-off to the addition of more sensors and more electronics while allowing for a field of view which is adequate for a particular application.